Monopole, Astrophysics and Cosmic Ray Observatory
Encyclopedia
MACRO, or the Monopole, Astrophysics and Cosmic Ray Observatory, is a particle physics
experiment located at the Laboratori Nazionali del Gran Sasso
in Abruzzo
, Italy
. A number of universities contributed personnel and equipment, including Boston University
and University of L'Aquila
.
The primary goal of MACRO is to search for magnetic monopoles. The active elements of MACRO are liquid scintillator
and streamer tubes, optimized for high resolution tracking and timing. This design also allows MACRO to operate as a neutrino
detector and as a cosmic ray
observatory.
The magnetic monopole is a theorized particle that has not yet been observed. It is a possible solution to Maxwell's equations
. One researcher claimed to have observed a monopole with a light-bulb-sized detector. The fact that a detector the size of multiple football pitch
es (MACRO) has not yet duplicated this feat leads most to disregard the earlier claim.
The MACRO project includes a large underground cavern, approximately 800 meters underground, which was further hollowed out and presently houses hundreds of long chambers filled with scintillating
fluid – a fluid that gives off photons when a charged or magnetic particle passes through it. At opposing ends of the chamber are a pair of photomultiplier
tubes. These tubes contain a number of small charged "plates." They look like flood lights, but they are collectors that can take a handful of photon
s and "multiply" them. This multiplication begins by using the photo-electric effect to convert photons that hit the first "plate" into electron
s. These electrons are then attracted to the next plate which gives off more electrons that it receives. The next plate does the same, thus amplifying the signal more at each plate. The photomultipliers used in the MACRO experiment were produced by Thorn-EMI, and are sensitive to a signal as small as five photons. After decommissioning, MACRO donated about 800 photomultiplier tubes to the Daya Bay Reactor Neutrino Experiment
. The exact voltage
put on each plate was determined by a custom circuit board designed by some of the scientists involved with the project. The project leader at Boston University was Prof. James Stone.
The scintillating chambers were assembled into high stacks and long rows. When a signal is detected, it is usually detected in multiple chambers. The timing of each signal from each photomultiplier tells the approximate path and speed of the particle. The type of signal and the speed through the "pool" of chambers tells researchers if they have observed a monopole or merely some common charged particle
.
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
experiment located at the Laboratori Nazionali del Gran Sasso
Laboratori Nazionali del Gran Sasso
Laboratori Nazionali del Gran Sasso is a particle physics laboratory of the INFN, situated near the Gran Sasso mountain in Italy, between the towns of L'Aquila and Teramo, about 120 km from Rome. In addition to a surface portion of the laboratory, there are extensive underground facilities...
in Abruzzo
Abruzzo
Abruzzo is a region in Italy, its western border lying less than due east of Rome. Abruzzo borders the region of Marche to the north, Lazio to the west and south-west, Molise to the south-east, and the Adriatic Sea to the east...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. A number of universities contributed personnel and equipment, including Boston University
Boston University
Boston University is a private research university located in Boston, Massachusetts. With more than 4,000 faculty members and more than 31,000 students, Boston University is one of the largest private universities in the United States and one of Boston's largest employers...
and University of L'Aquila
University of L'Aquila
The University of L'Aquila is a university located in L'Aquila, central Italy. It was founded in 1964 and is organized in nine faculties.Presents a scientific-technological character with many research groups. Its faculties occupy a high position between the Italian universities...
.
The primary goal of MACRO is to search for magnetic monopoles. The active elements of MACRO are liquid scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
and streamer tubes, optimized for high resolution tracking and timing. This design also allows MACRO to operate as a neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
detector and as a cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
observatory.
The magnetic monopole is a theorized particle that has not yet been observed. It is a possible solution to Maxwell's equations
Maxwell's equations
Maxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. These fields in turn underlie modern electrical and communications technologies.Maxwell's equations...
. One researcher claimed to have observed a monopole with a light-bulb-sized detector. The fact that a detector the size of multiple football pitch
Association football pitch
An association football pitch is the playing surface for the game of association football made of turf. Its dimensions and markings are defined by Law 1 of the Laws of the Game, "The Field of Play".All line markings on the pitch form part of the area which they define...
es (MACRO) has not yet duplicated this feat leads most to disregard the earlier claim.
The MACRO project includes a large underground cavern, approximately 800 meters underground, which was further hollowed out and presently houses hundreds of long chambers filled with scintillating
Scintillation
Scintillation can refer to:*Scintillation , atmospheric effects which influence astronomical observations*Interplanetary scintillation, fluctuations of radio waves caused by the solar wind...
fluid – a fluid that gives off photons when a charged or magnetic particle passes through it. At opposing ends of the chamber are a pair of photomultiplier
Photomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...
tubes. These tubes contain a number of small charged "plates." They look like flood lights, but they are collectors that can take a handful of photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s and "multiply" them. This multiplication begins by using the photo-electric effect to convert photons that hit the first "plate" into electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s. These electrons are then attracted to the next plate which gives off more electrons that it receives. The next plate does the same, thus amplifying the signal more at each plate. The photomultipliers used in the MACRO experiment were produced by Thorn-EMI, and are sensitive to a signal as small as five photons. After decommissioning, MACRO donated about 800 photomultiplier tubes to the Daya Bay Reactor Neutrino Experiment
Daya Bay Reactor Neutrino Experiment
The Daya Bay Reactor Neutrino Experiment is a China-based multinational particle physics project studying neutrinos. The multinational collaboration includes researchers from China, the United States, Taiwan, and the Czech Republic. The US side of the project is funded by the US Department of...
. The exact voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
put on each plate was determined by a custom circuit board designed by some of the scientists involved with the project. The project leader at Boston University was Prof. James Stone.
The scintillating chambers were assembled into high stacks and long rows. When a signal is detected, it is usually detected in multiple chambers. The timing of each signal from each photomultiplier tells the approximate path and speed of the particle. The type of signal and the speed through the "pool" of chambers tells researchers if they have observed a monopole or merely some common charged particle
Charged particle
In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...
.